Barometric or gravity induced flow oil level regulators have long been used to maintain oil in an engine crankcase at a desired predetermined level. In these systems an air tight oil reservoir is mounted at a level above the desired oil level in the crankcase and the reservoir is connected in fluid flow communication with the crankcase by an oil carrying conduit connected to a low point in the reservoir and an air carrying conduit connected to an air space above the oil level in the reservoir. In some cases, the same conduit carries both the oil and the air.
In a standpipe system the air and oil carrying conduit or conduits are connected to a sensing chamber outside the crankcase and the sensing chamber is in fluid flow communication with the crankcase. A portion of the standpipe sensing chamber is positioned above the desired oil level in the crankcase so that an air space exists above the oil level in the standpipe sensing chamber.
The air carryding conduit has an open end maintained within the sensing chamber at the level at which it is desired to maintain oil within the crankcase. When the oil level is low in the crankcase and consequently in the sensing chamber, air travels through the open end of the air carrying conduit and up the conduit to the reservoir to relieve a partial vacuum in the air space above the oil in the reservoir. Consequently oil commences to flow from the reservoir to the crankcase via the oil supply conduit. The oil flows until the open end of the air carrying conduit is covered or sealed by oil so that air can no longer flow to the air space in the reservoir.
The oil continues to flow until the pressure differential between the air pressure in the reservoir and the air pressure in the air space above the oil in the crankcase equals the head of oil in the supply line, at which time flow ceases until air can again flow through the air carrying conduit.
In prior art standpipe systems the air space in the sensing chamber has usually been vented to atmosphere. Although the crankcase is also vented to atmosphere, during engine operation the air pressure above the oil in the crankcase may not be the same as the atmospheric pressure in the air space in the sensing chamber due to blockages in the crankcase venting, such as a partially blocked road draft tube or positive crankcase ventilation valve and/or conditions such as worn piston rings which allow large amounts of combusted air/fuel charge gases which drive the pistons to bypass the cylinder wall/piston ring interface and escape into the crankcase.
U.S. Pat. No. 1,340,687 shows an oil level regulator system in which an air space in a standpipe is connected in fluid flow communication with the crankcase. In this patent a conduit connects the sensing chamber air space directly to the crankcase to circulate oil from the crankcase to the sensing chamber. Due to the oil flow in this conduit as well as air turbulence and localized windages present within the crankcase caused by moving engine components this conduit would not provide a dependable pressure equalizing vent between the crankcase air space and the sensing chamber air space during operation of the engine.